Passive fan assembly

ABSTRACT

A passive fan assembly includes an impeller and a plurality of guide blades disposed in front of the impeller. The impeller includes a plurality of blades extending at about 90 degrees relative to the guide blades. Thus, when airflow enters the passive fan assembly, the guide blades guide the airflow to effectively impact on blades of the impeller.

BACKGROUND

The invention relates to a passive fan assembly, and in particular, to a passive fan assembly provided with guide blades for increasing the kinetic energy received by the impeller of the assembly in operation and promoting the efficiency of energy transfer.

Generally, a fan is used together with a motor. The motor rotates the fan to dissipate heat.

A conventional fan presents the following drawbacks. A fan and a motor are generally used together, thus, a consumer must pay for the motor and the fan. The motor, coupled to a fan, occupies additional space even if the size of the motor is minimized. Moreover, if the components to be cooled are disposed in different locations in an electronic system, more than one fan and motor are required. More motors used in the electronic system indicate more power has to be provided and consumed, which does not conform to the trend of saving power.

Thus, a passive fan assembly capable of providing an improved heat-dissipating efficiency by effectively using airflow is desirable.

SUMMARY

The invention provides a passive fan assembly comprising a plurality of guide blades disposed in front of an impeller. The guide blades extend at about 90 degrees relative to blades of the impeller. Thus, in operation, the airflow passes through the guide blades, turns, and impacts on the blades of the impeller at about 90 degrees, thereby effectively rotating the impeller and promoting the heat-dissipating efficiency.

A passive fan assembly in accordance with an exemplary embodiment of the invention includes a base, an impeller connected to the base, and a cover disposed in front of the impeller and connected to the base.

The impeller includes a hub, a plurality of runner blades disposed around the hub, a partition connected to ends of the runner blades, a plurality of active blades disposed around the partition, and a rotary shaft axially extending from the hub.

The base includes a frame, a bearing seat, a plurality of connecting elements connecting the frame and the bearing seat, and a bearing disposed in the bearing seat for holding the rotary shaft of the impeller.

The cover includes a frame, a stationary part, a plurality of guide blades disposed around the stationary part, a stationary ring connected to ends of the guide blades, and a plurality of supporting elements connecting the stationary ring and the frame.

The guide blade of the cover extends at about 90 degrees relative to the runner blade of the impeller. Thus, in operation, the airflow passes through the guide blades, turns, and impacts the runner blades at about 90 degrees, which accordingly drives the active blades to rotate.

The passive fan assembly of the invention is capable of effectively using the airflow and promoting the heat-dissipating efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 is a perspective view of the passive fan assembly in accordance with the invention;

FIG. 2 is an exploded view of a passive fan assembly of FIG. 1;

FIG. 3 shows the arrangement of a guide blade and a runner blade of FIG. 2;

FIG. 4 is a sectional view of a passive fan assembly in accordance with the invention;

FIG. 5A is a velocity diagram of airflow entering a passive fan assembly, wherein the passive fan assembly has no guide blades;

FIG. 5B is a velocity diagram of airflow entering the passive fan assembly of the invention, wherein the passive fan assembly has guide blades.

DETAILED DESCRIPTION

Referring to FIGS. 1, 2 and 4, a passive fan assembly in accordance with an embodiment of the invention includes a base 1, an impeller 2 mounted on the base 1, and a cover 3 disposed in front of the impeller 2 and connected to the base 1.

The impeller 2 includes a hub 20, a plurality of runner blades 22 encircling the hub 20, a partition 24 connected to ends of the runner blades 22, a plurality of active blades 26 encircling the partition 24, and a rotary shaft 28 axially extending from the hub 20.

The base 1 includes a frame 10, a bearing seat 12, a plurality of ribs 14 connecting the frame 10 and the bearing seat 12, and at least one bearing 16 disposed in the bearing seat 12 for holding the rotary shaft 28 of the impeller 2. The bearing 16 may be a bushing bearing, a ball bearing, a magnetic bearing or any other bearing in which the rotary shaft 28 can be stably rotated. Furthermore, a plurality of airflow-guiding blades can be substituted for the ribs 14 in the base 1 to guide airflow.

The cover 3 includes a frame 30, a stationary part 32, a plurality of guide blades 34 disposed around the stationary part 32, a stationary ring 36 connected to ends of the guide blades 34, and a plurality of supporting elements 38 connecting the stationary ring 36 and the frame 30.

Referring to FIG. 3, the guide blade 34 of the cover 3 is approximately perpendicular to the runner blade 22 of the impeller 2. When passing through the guide blade 34, the airflow turns and impacts the runner blade 22 at about 90 degrees, which drives the active blades 26 to rotate.

When the passive fan assembly of the invention is used together with an airflow-providing system, the cover 3 of the passive fan assembly is connected to the airflow outlet 4 of an airflow-generating device (e.g. an axial fan or an air blower) in the airflow-providing system. In operation, high-pressure airflow generated by the airflow-generating device entirely enters the passive fan assembly through the guide blades 34. The guide blades 34 have inclined surfaces to change the direction of the airflow so that the airflow can effectively impact the runner blades 22 of the impeller 2.

The function of the guide blades 34 of the invention can be clearly explained by referring to FIGS. 5A and 5B. FIG. 5A is a velocity diagram of airflow entering a passive fan assembly, wherein the passive fan assembly has no guide blades. The airflow, generated by an airflow-generating device, is axial high-pressure airflow and has a velocity V_(in). The vector V₂ of velocity V_(in) determines the work done by the airflow on the runner blade 22, while no work is contributed by the vector V₁. It is therefore understood that a part of kinetic energy of the airflow is lost. FIG. 5B is a velocity diagram of airflow entering the passive fan assembly of the invention, wherein the passive fan assembly has guide blades 34. When the axial airflow passes through the guide blade 34, the velocity of the axial airflow changes from V_(in) to V_(in)′ which is approximately perpendicular to the runner blade 22. Then, the airflow can fully do work on the runner blade 22 so that the kinetic energy transferred from the runner blade 22 to the active blade 26 is maximized. Thus, the heat-dissipating efficiency of the active blade 26 is significantly improved.

In conclusion, the passive fan assembly of the invention is capable of effectively promoting the energy transfer and providing a better heat-dissipating efficiency.

While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

1. A passive fan assembly comprising: a base; an impeller mounted on the base and comprising a hub and a plurality of blades disposed around the hub; and a cover placed over the base and comprising a plurality of guide blades corresponding to the plurality of blades of the impeller.
 2. The passive fan assembly as claimed in claim 1, wherein each guide blade extends at an angle relative to the corresponding blade of the impeller.
 3. The passive fan assembly as claimed in claim 2, wherein the angle is approximately 90 degrees.
 4. The passive fan assembly as claimed in claim 1, wherein the impeller further comprises a plurality of active blades disposed around the plurality of blades.
 5. The passive fan assembly as claimed in claim 4, wherein the impeller further comprises a partition disposed between the plurality of blades and the active blades.
 6. The passive fan assembly as claimed in claim 1, wherein the base comprises a frame, a bearing seat for receiving at least one bearing therein, and a plurality of connecting elements connecting the frame and the bearing seat, and the impeller includes a rotary shaft extending into the bearing seat.
 7. The passive fan assembly as claimed in claim 1, wherein the cover further comprises a frame connected to the base, a stationary part around which the plurality of guide blades are disposed, a stationary ring connected to ends of the plurality of guide blades, and a plurality of supporting elements connecting the stationary ring and the frame.
 8. The passive fan assembly as claimed in claim 1, wherein the plurality of guide blades have inclined surfaces.
 9. The passive fan assembly as claimed in claim 1, wherein the passive fan assembly is driven by an airflow generated by an airflow-providing system, and the airflow passes through the plurality of guide blades into the passive fan assembly.
 10. The passive fan assembly as claimed in claim 9, wherein the airflow-providing system comprises an axial fan or an air blower.
 11. The passive fan assembly as claimed in claim 9, wherein the airflow-providing system comprises an airflow outlet connected to the cover of the passive fan assembly.
 12. A passive fan assembly comprising: a housing comprising a plurality of guide blades on a side thereof; an impeller installed in the housing, comprising a hub, a plurality of blades encircling the hub, a partition connected to ends of the plurality of blades, and a plurality of active blades encircling the partition.
 13. The passive fan assembly as claimed in claim 12, wherein the plurality of guide blades corresponds to the plurality of blades of the impeller.
 14. The passive fan assembly as claimed in claim 13, wherein each guide blade extends at an angle relative to the corresponding runner blade of the impeller.
 15. The passive fan assembly as claimed in claim 14, wherein the angle is approximately 90 degrees.
 16. The passive fan assembly as claimed in claim 12, wherein the housing further comprises a stationary part around which the plurality of guide blades are disposed, a stationary ring connected to ends of the plurality of guide blades, and a plurality of supporting elements connecting the stationary ring and the housing.
 17. The passive fan assembly as claimed in claim 12, wherein the plurality of guide blades have inclined surfaces.
 18. The passive fan assembly as claimed in claim 12, wherein the passive fan assembly is rotated by airflow generated from an airflow-providing system and the airflow passes through the plurality of guide blades into the passive fan assembly.
 19. The passive fan assembly as claimed in claim 18, wherein the airflow-providing system comprises an axial fan or air blower.
 20. The device as claimed in claim 18, wherein the airflow-providing system comprises an airflow outlet connected to the side of the housing. 